Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : Low Cycle Fatigue

Low Cycle Fatigue of Precipitation Hardened Aluminum Alloy

Dhafir S. Al-Fattal; Saif Khalid Mahmood

Engineering and Technology Journal, 2015, Volume 33, Issue 9, Pages 2146-2158

In this work, the influence of different heat treatments on the mechanical properties and fatigue life under low cycles of wrought 7075 aluminum alloy was experimentally investigated. The heat treatments included peak ageing (T6), over ageing (T73) and annealing (O).The flat fatigue specimens were subjected to constant reverse bending load. The tests were performed at the laboratory environment with a frequency of 23.6 Hz andat a stress ratio (R) of -1.For each temper, strain-life graphs were obtained for specimens with notches in the form of central cylindrical holes made by drilling. The fatigue resistance of specimens with notches was comparedto the results for notch-free specimens. It was observed that the presence of a stress raiser, such as a drilled hole, lowers the fatigue life for all tempers. However, the notch sensitivity of the fatigue life was different for each temper. The fatigue crack growth rate of T73 and annealed temper was investigated; the results showed that T73 treated sample exhibits higher crack growth resistance. Paris` equation was derived for each temper.

Low Cycle Fatigue Failure of AA7020 Aluminum Alloy at different heat treatments

Engineering and Technology Journal, 2010, Volume 28, Issue 19, Pages 982-998

The present work encompasses Low Cycle Fatigue (LCF) of
the Al-alloy AA7020 with three conditions; annealing, natural
aging and artificial aging. The LCF tests carried out using standard
specimens cantilever beam types. Optical Light Microscope (OLM)
and Scanning Electron Microscope (SEM) were employed to
examine the fracture features .The results confirmed that AA7020-
O sustained cyclic ha rdening, while 7020-T4 & 7020-T6
undergoing cyclic softening, therefore make the annealing
conditions more resistance to LCF. The values of fa tigue str ength
exponent (b) is varying from (-0.064) to (-0.14) and fatigue
ductility exponent (c) from (-0.554) to (-0.60), whereas these
values within the general limitation of the metals. The number of
transition cycle (NT) for annealing condition is more comparing to
the other conditions which emphasis that the annealing alloy will
withstand more cycles before introducing the plastic zone. The
information extracted from Engineering Stress-Strain curve; (σu/σy)
as well as strain harden exponent (n) can be need to estimate the
behavior of annealing and artificial alloy, while the natural aging
alloy will need LCF testing to definite the conducting because of
its "n" less than (1.2) and (σu/σy ) more than (1.4) .The SEM
examination districted many point of cracks initiation for the three
alloys at stresses more than Yield point. OLM investigation of the
cross-section of fracture surface indicated the dominating of
applied stress when it is more than Yield point of artificial aging
alloy. Where the stress concentration is the most important role for
annealing specimens because of companion of cycle strain